Magnetrons are used within the field of microwave technology for converting electrical energy into microwaves. For example, magnetrons are used as microwave sources in radar equipment, microwave ovens, and plasma lamps.
The power supply to a magnetron essentially consists of the voltage U that is applied between the anode and cathode (filament) of the magnetron, see FIG. 1, said voltage generally being called the anode voltage. This anode voltage may be of the order of a few kilovolts. The current I passing through the magnetron as a result of said voltage is generally called the anode current.
In order for the magnetron to operate properly, the emission of electrons from the filament of the magnetron needs to be sufficiently large to provide a stable generation of microwaves. Generally, it is therefore necessary to provide a filament current I.sub.f, at least during magnetron start-up, through the filament for heating thereof. The filament typically consists of a filament body having a surface coating which increases the capacity of the filament to emit electrons. The filament current is typically provided by a low voltage power source of about of a few volts.
When the magnetron emits output power, the filament is indirectly heated as a result of some electrons returning to the filament. If these electrons have sufficiently high energy, more free electrons will be generated by secondary emission. As a result, the filament current may often be removed once the magnetron is operating at full power.
Hence, it is suitable to adjust the filament current according to the current power level if the magnetron is to be operated at varying power.
Conventionally, such adjustment has been provided by experimentally determining which filament currents are suitable at different power levels and by storing such power-filament current-relations as a table or function in a filament current control unit (denoted FCC in FIG. 1). Using such a table or function, the filament current control unit adjusts the filament current based upon the current power level of the magnetron.